1. Field
The present invention relates generally to telecommunications, and, more specifically, to multi-carrier and multi-cell communications in wireless systems.
2. Background
A modern communication system is expected to provide reliable data transmission for a variety of applications, such as voice and data applications. In a point-to-multipoint communications context, known communication systems are based on frequency division multiple access (FDMA), time division multiple access (TDMA), code division multiple access (CDMA), and perhaps other multiple access communication schemes.
A CDMA system may be designed to support one or more CDMA standards, such as (1) the “TIA/EIA-95 Mobile Station-Base Station Compatibility Standard for Dual-Mode Wideband Spread Spectrum Cellular System” (this standard with its enhanced revisions A and B will be referred to as the “IS-95 standard”), (2) the “TIA/EIA-98-C Recommended Minimum Standard for Dual-Mode Wideband Spread Spectrum Cellular Mobile Station” (the “IS-98 standard”), (3) the standard sponsored by a consortium named “3rd Generation Partnership Project” (3GPP) and embodied in a set of documents including Document Nos. 3G TS 25.211, 3G TS 25.212, 3G TS 25.213, and 3G TS 25.214 (the “W-CDMA standard”), (4) the standard sponsored by a consortium named “3rd Generation Partnership Project 2” (3GPP2) and embodied in a set of documents including “TR-45.5 Physical Layer Standard for cdma2000 Spread Spectrum Systems,” the “C.S0005-A Upper Layer (Layer 3) Signaling Standard for cdma2000 Spread Spectrum Systems,” and the “TIA/EIA/IS-856 cdma2000 High Rate Packet Data Air Interface Specification” (the “cdma2000 standard” collectively), (5) the 1xEV-DO standard, and (6) certain other standards. The standards listed above are incorporated by reference as if fully set forth herein, including annexes, appendices, and other attachments.
Multi-carrier communication systems are being developed to satisfy the constantly increasing demand for wireless services, and in particular for data services. A multi-carrier communication system is a system with the capability to transmit information on two or more carrier frequencies. It should be noted that multi-carrier system capability may exist in both downlink and uplink connections; alternatively, a multi-carrier system may have multi-carrier capability only on uplink or only on downlink. “Downlink” signifies forward direction of information transmission, i.e., transmission from the radio network to user equipment (“UE”), such as a cellular telephone, PDA, or computer. “Uplink” signifies transmission of information in the reverse direction, i.e., from the UE to the radio network.
Importantly, the number of forward link carriers may differ from the number of reverse link carriers in a multi-carrier system. For example, the number of downlink carriers (N) may exceed the number of uplink carriers (M), i.e., N>M. The opposite relationship is also possible, albeit less likely, with the number of uplink carriers exceeding the number of downlink carriers, i.e., M>N. Of course, the numbers of the uplink and downlink carriers may be the same in a multi-carrier system, i.e., N=M. As noted in the immediately preceding paragraph, either N or M may equal 1 in a multi-carrier system.
When the number of uplink carriers is equal to the number of downlink carriers (N=M) in a multi-carrier system, the uplink and downlink carriers may be “paired” in a manner similar to that of a single-carrier system, i.e., each uplink/downlink carrier can be paired with a corresponding downlink/uplink carrier. For two paired carriers, overhead (i.e., non-payload or control) information for the downlink carrier is carried by the paired uplink carrier, and overhead information for the uplink carrier is carried by the downlink carrier. When the number of uplink carriers is not the same as the number of downlink carriers (N≠M), one or more “unpaired” carriers may result either on the downlink or on the uplink. In such asymmetric multi-carrier communication systems signaling needs to be adapted so that overhead information is transmitted for the unpaired carriers.
When upgrading previously-deployed communication systems, it is desirable to maintain backward compatibility with legacy equipment. For example, it would be desirable to maintain compatibility of existing cellular telephones when upgrading the radio network. Furthermore, changes to previously-deployed communication systems should preferably be put into place via software upgrades, while minimizing the need for hardware changes. These observations hold equally true when upgrading a wireless communication system from single-carrier to multi-carrier capability.
There is therefore a need in the art for methods and apparatus that preserve backward compatibility of user equipment and reduce the necessity for hardware changes when adding multi-carrier capability to single-carrier communication systems. In particular, a need exists in the art for methods and apparatus that provide signaling for unpaired carriers in multi-carrier systems while preserving compatibility with user equipment designed for single-carrier operation, and while reducing the need for hardware changes in the radio network.